Clean up vp9_firstpass.h
Clean up vp9_firstpass.h

Remove unused functions and macros.

Change-Id: I46458a60f75637c66af0e18ad876a2634e5818bb

webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx